This invention relates to a method for the detection of a particular motile organism in a sample, for example flagellate bacteria such as Salmonella.
Salmonella is a genus of aerobic gram-negative flagellate bacteria which may be found in a variety of foodstuffs and which are a cause of various pathological conditions in man. Salmonellosis is a major problem in the United States because of its incidence, economic significance and hazardous nature. Salmonellosis is usually not a fatal disease but there have been fatalities reported in infants and the aged.
Food and feed industries intensively scrutinize their products for Salmonella contamination because of the fear of having to recall and destroy contaminated products. However, in the early stages of food processing, while the foodstuff is within the possession and control of the manufacturer, the Salmonella is commonly present in only a minute amount. Further complicating the task of detection of the Salmonella is the presence of numerous other microorganisms including competitive flagellate species typically present in foodstuffs and animal feeds.
There are a number of disadvantages associated with the conventional detection procedures for Salmonella. The cultural procedures are cumbersome and labor-intensive to perform, require expensive laboratory materials, are lengthy, requiring up to four days to complete, and may yield false negative results. The fluorescent antibody technique requires highly trained personnel, expensive fluorescent microscopic systems and costly fluorescein-labeled antisera, which at times lack specificity.
Several attempts have been made to devise other rapid and simple methods for the detection of Salmonella. Many of these methods involve preferential migration of Salmonella through a selective semi-solid motility medium. Mohit et al. in "A Simple Single-Step Immunoimmobilization Method for the Detection of Salmonella in the Presence of Large Numbers of Other Bacteria," J. Med. Microbiol., Vol. 8, page 173 (1975) and Swaminathan et al in "Rapid Detection of Salmonella in Foods by Membrane Filter-Disc Immobilization Technique," J. Food Science, Vol. 43, No. 5, p. 1444 (1978) described selective semi-solid media which promoted the migration of Salmonella in a petri dish followed by immobilization using polyvalent H antisera. Swaminathan et al using a membrane filter to concentrate Salmonella from the primary selective enrichment before selective migration in order to increase recovery.
Although these motility techniques showed promise, operational difficulties compromised their effectiveness. Some problems of note included:
(1) the lack of definite and easily interpretable reactions to indicate the presence of Salmonella;
(2) the use of chemical agents in the motility medium to promote the selective migration of Salmonella which greatly reduced or completely inhibited motility of certain Salmonella strains; and
(3) the use of intricate glassware arrangements which made setup and inoculation difficult and expensive.
Accordingly, it is a principal object of the present invention to develop an improved motility method for detecting Salmonella or other particular motile organisms in a sample.
It is another object of the present invention that such improved method be sensitive and specific.
It is a further object of the present invention that such improved method be rapid, microbiologically safe, uncomplicated and inexpensive.
It is a still further object of the present invention that such improved method contain a definite and easily interpretable indication of the presence of Salmonella or other particular motile organisms to be detected.